Removable bar for current transformer



g- 2, 1966 F. R. D'ENTREMONT 3,264,591

REMOVABLE BAR FOR CURRENT TRANSFORMER Filed D80. 51. 1963 2 Sheets-Sheet 1 [72 @2257" h m/M72 1?. 35256222022]:

g- 2, 1966 F. R. DENTREMONT 3,264,591

REMOVABLE BAR FOR CURRENT TRANSFORMER Fi led Dec. 31. 1963 2 Sheets-Sheet 2 United States Patent 3,264,591 REMOVABLE BAR FOR CURRENT TRANSFORMER Franklin R. DEntremont, Dover, NJi-L, assignor to General Electric Company, a corporation of New York Filed Dec. 31, 1963, Ser. No. 334,833 3 Claims. (Cl. 336-174) This invention relates to current transformers and more particularly to removable primary bars for current transformers.

As is well known to those skilled in the current transformer field, current transformers are usually of two types; either a window transformer or a primary bar transformer. In the window type construction no primary winding is supplied. A line conductor passing through the window of the transformer serves as the primary. In the primary bar type a primary bar is provided placed in the window of the current transformer. The primary bar is connected to line conductors and serves as the primary of the current transformer.

Current transformers are used to transform large line currents to very small currents to enable metering and measuring of the current in the line. The particular type of current transformer used will depend on the type of installation on which it is to be connected. In general, most current transformers are made either as window types or as primary bar types. Since current transformers must be used on a variety of installations, utilities and other users of current transformers are required to maintain a sufificient quantity of both types of transformers in stock to meet any foreseeable need. Obviously, it is desirable to reduce as much as possible the need for stocking duplicate types of transformers; that is, transfromers of the same class in both Window type and primary bar type. It will be clear from the above that it is desirable to provide current transformers with removable primary bars so that the same transformer may be used either as a window type or as a primary bar type. With this construction, it would only be necessary to stock window transformers of any particular class and a plurality of removable primary bars for adapting the window type transformer to a primary bar type transformer. Of course, it will be readily understood that the removable primary bar must make a very snug fit with the window opening of the window type transformer in order to prevent turning and twisting of the primary bar, and to prevent the primary bar from shifting within the window opening.

Therefore, it is a primary object of this invention to provide a removable primary bar for current transformers.

It is a further object of this invention to provide a removable primary bar for current transformers in which the primary bar is provided with a bushing member which makes a snugfit with the window opening of a current transformer.

A still further object of this invention is to provide a current transformer having a primary bar installed in the window opening with the primary bar being readily removable from such window opening.

It has previously been proposed to provide a primary bar for a current transformer wherein the bar is adjustable within the window opening and is held therein by a friction fit. See Patent Number 2,815,493. However, in that construction the primary bar is cylindrical and the entire length of the bar in the transformer forms a tight friction fit with the casing forming the window of the transformer. construction makes it very difiicult to insert or remove the primary bar from the current transformer. Recently, it has been discovered that if the primary is a flat bar member and is provided with a resilient serrated bushing, wherein only the serrations are adequately dimensioned to provide a'tight friction fit with the window opening, that the primary bar may be readily moved into and removed from the Window of the transformer. The flexible or resilient serrations provide a very tight fit, holding the primary bar securely in the transformer against any accidental movement due to vibrations or the like. However, when it is desired to remove the primary bar, the flexible or resilient serrations readily respond to pressure to flex and allow the primary bar to be moved as desired.

In carrying out this invention in one form, a primary bar is provided for a current transformer. The primary bar is made of .a flat, electrically conducting member, such as copper, and a serrated bushing of insulating material is secured to the center portion of the primary bar. The serrations of the insulating bushing have an external diameter which is slightly greater than the window opening of the current transformer such that the primary b'ar may be inserted in the window opening and the serrations Will hold the primary bar firmly in such window opening.

The invention which it is desired to protect will be particularly pointed out and distinctly claimed in the claims appended hereto. However, his believed that this invention and the manner in which its various objects and advantages are obtained, as well as other objects and advantages thereof, will be more fully understood by reference to the following detailed description of preferred embodiments thereof especially when considered in conjunction with the accompnaying drawings, in which:

FIGURE 1 is a perspective view of one form of a window type current transformer;

FIGURE 2 is a perspective view of one form of removable primary bar according to this invention suitable for use with the transformer of FIG. 1;

' FIGURE 3 is a perspective view of a modified formof removable primary bar according to this invention also suitable for use with the transformer of FIG. 1; and

FIGURE 4 is a perspective view of the current transformer of FIG. 1 showing a removable primary bar, such as'the bar of FIG. 2 or 3 assembled therewith.

Reference will now be made to the drawings in which like numerals are used to indicate like parts throughout the various views thereof. Referring first to FIG. 1 of the drawing, there is shown, in perspective view, one form of'a window type current transformer 10. The current transformer 10 comprises a molded body member 12 which may be for example of butyl rubber which encloses a secondary winding (not shown) and has secondary terminals 14 formed at the top of body member 12. A window opening 16 is formed through body member 12, as is well understood, providing the means for inserting a line conductor as a primary through the transformer, inductively coupled with the secondary of the transformer 10. A base member 18 is provided secured to body member 12 by a metal plate 20 which is wrapped Patented August 2, 1966 It has been found that this type of about body member 12 in the manner shown. The current transformer of FIG. 1 is a conventional transformer and, as such, forms no part of the invention. However, the invention is useful with the type of current transformer shown in FIG. 1 and also may be used with similar types of current transformers as will be understood from the following description.

The window type current transformer 10 may be converted to a primary bar type by means of a removable primary bar, such as that shown in FIGS. 2 and 3 of the drawings. Considering first FIG. 2, there is shown a perspective view of a removable primary bar 22. The removable primary bar 22 comprises a flat, electrical conducting bar member 24 having a serrated bushing member 26 secured to the center portion of bar 24. The bushing member 26 may be a single piece molded about the center portion of bar 24, or it may be two separate pieces secured to the center portion of primary bar 24 by molding or by use of any known adhesive material. In the preferred embodiment shown in FIG. 2, bushing 26 is made in two parts, 28 and 30, with each part being provided with a plurality of serrations 32. The serrations 32 extend transversely of bushing 36 as shown. Bushing 26 is desirably made from a type of flexible insulating material, such as, for example, butyl rubber. The serrations 32 having an outer diameter which is preferably slightly larger than the window opening of the transformer, for example the window 16 of the transformer 10. The serrations 32 are made of a flexible material such as butyl rubber, and as can be seen from FIG. 2 they are relatively thin as compared to the over-all length of bushing 26. When the removable primary bar 22 is inserted in the Window opening the serrations 32 will bend slightly to enable the bar to be inserted in the window opening, such as opening 16. Obviously, due to the flexibility of the serrations 32 the primary bar 22 will snugly fit within the Window opening and will be firmly fixed thereto due to the flexible serrations 32. Of course, inasmuch as serrations 32 are flexible it will be understood that, if desired, the bar 22 may be later removed from the window opening again converting the transformer to a window type current transformer. Various openings 34 may be provided in the end portions of bar 24 for securing line conductors thereto.

Referring now to FIG. 3 of the drawings, there is shown a perspective view of another type of removable primary bar, indicated at 22'. As shown in FIG. 3, the primary bar 22' also comprises a flat, electrical conducting bar member 24 having the serrated bushing member 26 secured to the center portion thereof. The bushing 26 is also shown as being formed of two separate parts, 28 and 30', each being secured to one side of the center portion of the primary bar 24, such as for example by molding. Each of the bushing parts 28' and 30' is provided with a plurality of serrations 36, the serrations being provided with a straight side and a sloping side in the manner shown. The serrations 36 extend transversely of bushing 26' as shown. As will be understood, since the bushing 26 is made of a flexible material, such as for example butyl rubber, the serrations 36 will be provided with a flexibility to allow them to give slightly when inserted in the window opening of a current transformer. Of course it will be understood that the outer diameter of the serrations 36 will preferably be of a slightly larger diameter than the window opening to allow a snug fit. Due to the sloping of the serrations 36 the bar 24 may be inserted into the window opening, in the direction indicated by the arrows, which will force the sloping sides of the serrations 36 against the interior of the window opening allowing the primary bar 22' to be forced into such window opening. Due to the straight sides it will be relatively diflicult to remove the primary bar in a direction opposite to that of the arrows since the straight sides will tend to bind against the sides of the window opening.

However, as will be understood, due to the-sloping side of the serrations 36 the primary bar may be easily moved out of the window opening by continuing movement in the direction of the arrows on the flat bar member 24'. In the same manner as shown with reference to FIG. 2, various openings 34' are provided on the bar member 24' for making any desired connection to the line conductor to which the primary bar member 22 is to be connected.

FIGURE 4 of the drawing shows the current transformer 10 of FIG. 1 having a removable primary bar, such as the bar of FIG. 2, inserted within the window opening 16. As will be apparent from FIG. 4 of the drawings, the bushing member 26 on primary bar 22 snugly fits within the window opening 16 and firmly holds the primary bar 22 therein. Thus it can be seen from FIG. 4 that the window type current transformer 10 of FIG. 1 has been converted into a primary bar type current transformer by means of the removable primary bar of either FIG. 2 or FIG. 3. Of course it will be clear that, if desired, the primary bar 22 may be removed from the window opening 16 and the transformer 10 converted again to a window type current transformer. Thus it will be apparent that by means of the removable primary bar of this invention it is possible to convert a window type current transformer to a primary bar type and thereby dispense with the necessity of maintaining in stock a plurality of transformers of each type in the same class.

While there has been shown and described the present preferred embodiments of this invention it will, of course, be readily apparent to those skilled in the art that many changes may be made in the constructional details of the removable primary bar without departing from the spirit and scope of the invention, especially as set forth in the appended claims.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. A primary bar type current transformer comprising, in combination, a window type current transformer having a window opening therein, a removable primary bar mounted in said window opening, said removable primary bar comprising a flat, electrical conducting member having a serrated bushing of flexible insulating material secured to the central portion of said flat conducting member, said serrations of said bushing extending transversely of said bushing and contacting the walls of said window opening to removably secure said primary bar member in said window opening.

2. A primary bar type current transformer comprising, in combination, a window type current transformer having a window opening therein, a removable primary bar mounted in said window opening, said removable primary bar comprising a flat, electrical con-ducting member having a serrated bushing of flexible insulating material secured to the central portion of said flat conducting member, said serrations of said bushing extending transversely of said bushing and having a straight side and a sloping side, with the outer diameter of said serrations being slightly larger than the inner diameter of said window opening, said serrations of said bushing contacting the walls of said window opening to removably secure said primary bar member in said window opening.

3. A primary bar type current transformer comprising, in combination, a window type current transformer having a window opening therein, a removable primary bar mounted in said window opening, said removable primary bar comprising a flat, electrical conducting member having a serrated bushing of flexible insulating material secured to the central portion of said flat conducting member, said serrations of said bushing extending transversley of said bushing and having straight sides with the outer diameter of said serrations being slightly larger than the inner diameter of said window opening, said serrations of said bushing contacting the walls of said window opening to removably secure said primary bar member in said Window opening.

(References on following page) References Cited by the Examiner OTHER REGFERENCES UNITED STATES PATENTS Spelsberg, German application No. 1,137,490, pub. 2,704,355 3/1955 HoTton 174 77x (kt-4,1962- 3132333? 551321 %ilteaiiiiiiiiiiii13315; 5 LEWIS MYERS Pfimm 3,082,389 3/1963 Settles et a1 336174 ROBERT SCHAEFER, LARAMIE fL FOREIGN PATENTS Exammm' 824,655 12/1951 Germany. D. J. BADER, Assistant Examiner. 

1. A PRIMARY BAR TYPE CURRENT TRANSFORMER COMPRISING, IN COMBINATION, A WINDOW TYPE CURRENT TRANSFORMER HAVING A WINDOW OPENING THEREIN, A REMOVABLE PRIMARY BAR MOUNTED IN SAID WINDOW OPENING, SAID REMOVABLE PRIMARY BAR COMPRISING A FLAT, ELECTRICAL CONDUCTING MEMBER HAVING A SERRATED BUSHING OF FLEXIBLE INSULATING MATERIAL SECURED TO THE CENTRAL PORTION OF SAID FLAT CONDUCTING MEMBER, SAID SERRATIONS OF SAID BUSHING EXTENDING TRANSVERSELY OF SAID BUSHING AND CONTACTING THE WALLS OF SAID WINDOW OPENING TO REMOVABLY SECURE SAID PRIMARY BAR MEMBER IN SAID WINDOW OPENING. 